Vue 实例挂载的实现
在执行new Vue时,vue会去判断是否定义的了el参数,去执行$mount去挂载vm
$mount
// 在src/core/instance/init.js中
if (vm.$options.el) {
vm.$mount(vm.$options.el)
}
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重写原型上的$mount方法
纯前端浏览器环境compiler版本的$mount
- 如果el指向body或者html根节点则报错
- 判断当前实例有没有定义render函数,如果没有就去取template,通过compileToFunctions方法转换出render方法
- 最后去调用原型上mount方法
// src/platform/web/entry-runtime-with-compiler.js
const mount = Vue.prototype.$mount
Vue.prototype.$mount = function (
el?: string | Element,
hydrating?: boolean
): Component {
el = el && query(el)
/* istanbul ignore if */
if (el === document.body || el === document.documentElement) {
process.env.NODE_ENV !== 'production' && warn(
`Do not mount Vue to <html> or <body> - mount to normal elements instead.`
)
return this
}
const options = this.$options
// resolve template/el and convert to render function
if (!options.render) {
let template = options.template
if (template) {
if (typeof template === 'string') {
if (template.charAt(0) === '#') {
template = idToTemplate(template)
/* istanbul ignore if */
if (process.env.NODE_ENV !== 'production' && !template) {
warn(
`Template element not found or is empty: ${options.template}`,
this
)
}
}
} else if (template.nodeType) {
template = template.innerHTML
} else {
if (process.env.NODE_ENV !== 'production') {
warn('invalid template option:' + template, this)
}
return this
}
} else if (el) {
template = getOuterHTML(el)
}
if (template) {
/* istanbul ignore if */
if (process.env.NODE_ENV !== 'production' && config.performance && mark) {
mark('compile')
}
const { render, staticRenderFns } = compileToFunctions(template, {
outputSourceRange: process.env.NODE_ENV !== 'production',
shouldDecodeNewlines,
shouldDecodeNewlinesForHref,
delimiters: options.delimiters,
comments: options.comments
}, this)
options.render = render
options.staticRenderFns = staticRenderFns
/* istanbul ignore if */
if (process.env.NODE_ENV !== 'production' && config.performance && mark) {
mark('compile end')
measure(`vue ${this._name} compile`, 'compile', 'compile end')
}
}
}
return mount.call(this, el, hydrating)
}
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原型$mount的实现
原型上的$mount方法定义在 src/platforms/web/runtime/index.js中,实际上是调用了mountComponent方法, 这个方法定义在src/core/instance/lifecycle.js中
传入2个参数,第一个是el,它表示挂载的元素,可以是字符串,也可以是DOM对象,如果是字符串在浏览器环境下会调用query方法转换成DOM对象的.第二个参数是和服务端渲染相关,在浏览器环境下我们不需要传第二个参数
// public mount method
Vue.prototype.$mount = function (
el?: string | Element,
hydrating?: boolean
): Component {
el = el && inBrowser ? query(el) : undefined
return mountComponent(this, el, hydrating)
}
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mountComponent方法
- 如果options上没有render方法,就创建空的VNode
- 执行beforeMount钩子
- 定义updateComponent方法,实际上是调用vm._update去触发更新
- 实例化一个渲染Watcher,用来监听更新,在before钩子中添加了beforeUpdate钩子函数,在组件生成后,销毁前会去执行beforeUpdate钩子
- 第一次编译时$vnode为null,把实例的_isMounted设置为true,执行mounted钩子
export function mountComponent(
vm: Component,
el: ?Element,
hydrating?: boolean
): Component {
vm.$el = el
if (!vm.$options.render) {
vm.$options.render = createEmptyVNode
if (process.env.NODE_ENV !== 'production') {
/* istanbul ignore if */
if ((vm.$options.template && vm.$options.template.charAt(0) !== '#') ||
vm.$options.el || el) {
warn(
'You are using the runtime-only build of Vue where the template ' +
'compiler is not available. Either pre-compile the templates into ' +
'render functions, or use the compiler-included build.',
vm
)
} else {
warn(
'Failed to mount component: template or render function not defined.',
vm
)
}
}
}
callHook(vm, 'beforeMount')
let updateComponent
/* istanbul ignore if */
if (process.env.NODE_ENV !== 'production' && config.performance && mark) {
updateComponent = () => {
const name = vm._name
const id = vm._uid
const startTag = `vue-perf-start:${id}`
const endTag = `vue-perf-end:${id}`
mark(startTag)
const vnode = vm._render()
mark(endTag)
measure(`vue ${name} render`, startTag, endTag)
mark(startTag)
vm._update(vnode, hydrating)
mark(endTag)
measure(`vue ${name} patch`, startTag, endTag)
}
} else {
updateComponent = () => {
vm._update(vm._render(), hydrating)
}
}
// we set this to vm._watcher inside the watcher's constructor
// since the watcher's initial patch may call $forceUpdate (e.g. inside child
// component's mounted hook), which relies on vm._watcher being already defined
new Watcher(vm, updateComponent, noop, {
before() {
if (vm._isMounted && !vm._isDestroyed) {
callHook(vm, 'beforeUpdate')
}
}
}, true /* isRenderWatcher */)
hydrating = false
// manually mounted instance, call mounted on self
// mounted is called for render-created child components in its inserted hook
if (vm.$vnode == null) {
vm._isMounted = true
callHook(vm, 'mounted')
}
return vm
}
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